JP7081147B2 - How to make a golf ball - Google Patents

Description

The present invention relates to a method for manufacturing a golf ball.

Conventionally, a golf ball having a spherical core formed from a rubber composition and a cover covering the spherical core has been proposed. Golf balls are usually used repeatedly. Therefore, the golf ball is required to have durability against hitting. As a method for improving the hitting durability of a golf ball, it has been proposed to add a polyfunctional compound to the rubber composition constituting the core.

For example, in Patent Document 1, polybutadiene is used as a base material, and a mixture of a polyfunctional unsaturated ester and an unsaturated carboxylic acid is added and blended as a polymerization crosslinkable monomer, and the compounding amount of the polymerization crosslinkable monomer is polybutadiene. A golf ball compound having 20 to 35 parts by weight with respect to 100 parts by weight is described (see Patent Document 1 (claims 1, Tables 1 and 2)).

Further, Patent Document 2 describes 100 parts by weight of polybutadiene rubber, 15 to 25 parts by weight of acrylic acid or methacrylic acid, 1 to 15 parts by weight of an ester of acrylic acid or methacrylic acid, 20 to 70 parts by weight of zinc oxide, and organic peroxide. A solid core formed by heating and cross-linking a composition containing 1 to 6 parts by weight of a substance to a diameter of 36.5 mm to 39.0 mm, 100 parts by weight of an ionomer resin, and 0.5 to 10 metal salts of acrylic acid or methacrylic acid. A golf ball is described in which a composition containing 1 to 5 parts by weight of a colorant and 1 to 5 parts by weight is coated with a thickness of 1.8 mm to 2.3 mm (see Patent Document 2 (Claim 1 and Table 1)). ).

Japanese Unexamined Patent Publication No. 57-25337 Japanese Unexamined Patent Publication No. 58-118775

When a crosslinkable compound having two or more polymerizable unsaturated bonds is blended in the rubber composition constituting the core, the crosslinkable compound may be polymerized independently by heat at the time of core molding. If the amount of homopolymerization by such a crosslinkable compound increases, the formation of three-dimensional crosslinks by the crosslinkable compound becomes insufficient, and the effect of improving the impact durability of the core may not be obtained.

The present invention has been made in view of the above circumstances, and is a homopolymerization of the crosslinkable compound in a method for producing a golf ball using a rubber composition containing a crosslinkable compound having two or more polymerizable unsaturated bonds. It is an object of the present invention to provide a manufacturing method for obtaining a golf ball having excellent impact durability.

The method for producing a golf ball of the present invention is a method for producing a golf ball having a spherical core and at least one layer or more of a cover covering the spherical core, wherein (a) a base rubber and (b) a co-crosslinking agent. Α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or a metal salt thereof, (c) a crosslinkable compound having two or more polymerizable unsaturated bonds in the molecule, and (d) initiation of cross-linking. The first step of kneading the agent to prepare a rubber composition for a core, the second step of producing a spherical core at a molding temperature of 100 ° C. to 150 ° C. using the rubber composition for a core, and the spherical core. It is characterized by having a third step of forming at least one layer of a cover covering the spherical core.

In the method for producing a golf ball of the present invention, by controlling the core molding temperature in the range of 100 ° C. to 150 ° C., (c) homopolymerization of the crosslinkable compound due to heat can be suppressed. As a result, the obtained core is sufficiently formed with a three-dimensional crosslinked structure (c) by the crosslinkable compound, and the impact durability is improved.

According to the present invention, a golf ball having excellent hitting durability can be obtained.

A partially cutaway sectional view showing a golf ball according to an embodiment of the present invention.

The method for producing a golf ball of the present invention has a spherical core and at least one layer of a cover covering the spherical core, and the spherical core has at least (a) a base rubber and (b) carbon atoms as a cocrosslinking agent. 3-8 α, β-unsaturated carboxylic acids and / or metal salts thereof, (c) a crosslinkable compound having two or more polymerizable unsaturated bonds in the molecule, and (d) a crosslink initiator. It is a manufacturing method for producing a golf ball formed from the contained rubber composition for a core (hereinafter, may be simply referred to as "rubber composition").

The method for producing a golf ball of the present invention includes a first step of preparing a rubber composition, a second step of heating and pressing the rubber composition to form a spherical core, and forming at least one or more covers on the spherical core. It has a third step to be performed.

(1) First Step In the first step, (a) a base rubber, (b) an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms as a cocrosslinking agent and / or a metal salt thereof, (c). ) A crosslinkable compound having two or more polymerizable unsaturated bonds in the molecule and (d) a crosslink initiator are kneaded to prepare a rubber composition. In the present invention, "kneading" means that several kinds of compounding materials having different properties are mixed and dispersed with respect to the base rubber by applying a mechanical shearing force based on the compounding of the rubber composition. ..

In the first step, when kneading the compounding materials, all the compounding materials may be kneaded at once, or a part of the compounding materials may be kneaded and then the remaining compounding materials may be kneaded. It is preferable to knead the compounding material using a known kneader such as a roll, a kneader, or a Banbury mixer. From the viewpoint of increasing the kneading efficiency, it is preferable to use a kneader or Banbury mixer having a large shearing force.

The kneading temperature at the time of preparing the rubber composition is preferably 95 ° C. or higher, more preferably 100 ° C. or higher, preferably 125 ° C. or lower, and more preferably 120 ° C. or lower. When the kneading temperature is 95 ° C. or higher, the compounding material can be dispersed more uniformly, the performance of the compounding material is more exhibited, and when the kneading temperature is 125 ° C. or lower, the burning of the compounding material can be suppressed.

The kneading time for preparing the rubber composition is preferably 1 minute or more, more preferably 1.5 minutes or more, preferably 20 minutes or less, and more preferably 15 minutes or less. If the kneading time is within the above range, the compounding material can be uniformly dispersed.

In the first step, as an embodiment of kneading the compounding materials, all the compounding materials are kneaded at once to prepare a rubber composition (aspect 1); components other than the component (c) are kneaded to prepare a mixture. After the preparation, the mixture is kneaded with the component (c) to prepare a rubber composition (Aspect 2); the components other than the components (c) and (d) are kneaded to prepare a mixture, and then the mixture is prepared. Examples thereof include an embodiment (aspect 3) in which the mixture is kneaded with the component (c) and the component (d) to prepare a rubber composition. When the 1-minute half-life temperature of the component (d) is less than 160 ° C., it is preferable to adopt the third aspect.

In the cases of the above aspects 2 and 3, for example, (a) a base rubber, (b) an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or a metal salt thereof as a co-crosslinking agent, and a necessary After kneading the additives to be blended according to the above to prepare a mixture, the mixture is kneaded with the component (c) or the components (c) and (d) to prepare a rubber composition. By kneading the component (a), the component (b) and the additive in advance, the kneading temperature thereof can be set high, and the compounding material can be kneaded more uniformly.

The kneading temperature at the time of preparing the mixture is preferably 95 ° C. or higher, more preferably 100 ° C. or higher, preferably 125 ° C. or lower, and more preferably 120 ° C. or lower. When the kneading temperature is 95 ° C. or higher, the compounding material can be dispersed more uniformly, the performance of the compounding material is more exhibited, and when the kneading temperature is 125 ° C. or lower, the burning of the compounding material can be suppressed.

The kneading time for preparing the mixture is preferably 1 minute or more, more preferably 1.5 minutes or more, preferably 20 minutes or less, and more preferably 15 minutes or less. If the kneading time is within the above range, the compounding material can be uniformly dispersed.

It is preferable to knead the mixture using a known kneader such as a roll, a kneader, or a Banbury mixer. From the viewpoint of increasing the kneading efficiency, it is preferable to use a kneader or Banbury mixer having a large shearing force.

In the above aspects 2 and 3, the kneading temperature (T1) when preparing the rubber composition is preferably 20 ° C. or higher, more preferably 30 ° C. or higher, still more preferably 40 ° C. or higher, and preferably 110 ° C. or lower. It is more preferably 100 ° C. or lower, still more preferably 90 ° C. or lower. When the kneading temperature is 20 ° C. or higher, the component (c) can be uniformly dispersed, and when the kneading temperature is 110 ° C. or lower, the homopolymerization of the component (c) due to heat can be suppressed.

In the above embodiments 2 and 3, the temperature difference (Tc—T1) between the kneading temperature (T1) when preparing the rubber composition and the homopolymerization temperature (Tc) due to the heat of the (c) crosslinkable compound is 10 ° C. The above is preferable, more preferably 15 ° C. or higher, still more preferably 20 ° C. or higher. If the temperature difference (Tc-T1) is 10 ° C. or higher, even if heat is generated due to the shearing of the rubber, (c) homopolymerization due to the heat of the crosslinkable compound can be suppressed. The upper limit of the temperature difference (Tc-T1) is not particularly limited, but is preferably about 200 ° C.

In the third aspect, the temperature difference (Td—T1) between the kneading temperature (T1) when preparing the rubber composition and the one-minute half-life temperature (Td) of the (d) cross-linking initiator is 40 ° C. or higher. It is preferably more preferably 45 ° C. or higher, still more preferably 50 ° C. or higher. When the temperature difference (Td-T1) is 40 ° C. or higher, the decomposition of (d) the cross-linking initiator during the kneading of the rubber composition preparation can be suppressed. The upper limit of the temperature difference (Td—T1) is not particularly limited, but is about 140 ° C. When two or more kinds of the component (d) are used as the compounding material, it is preferable that the above range is satisfied for all the components (d).

In the above-mentioned aspects 2 and 3, the kneading when preparing the rubber composition can be performed by using a known kneader such as, for example, a roll, a kneader, or a Banbury mixer. From the viewpoint of suppressing heat generation of the compounding material during kneading, it is preferable to use a roll.

Hereinafter, the compounding materials will be described. In the method for producing a golf ball of the present invention, the rubber composition comprises at least (a) a base rubber, (b) an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms as a co-crosslinking agent and / or the same thereof. A metal salt, (c) a crosslinkable compound having two or more polymerizable unsaturated bonds in the molecule, and (d) a crosslink initiator are blended.

(A) Base material rubber As the (a) base material rubber, natural rubber and / or synthetic rubber can be used, for example, polybutadiene rubber, natural rubber, polyisoprene rubber, styrene polybutadiene rubber, ethylene-propylene-. Diene rubber (EPDM) or the like can be used. These may be used alone or in combination of two or more. Among these, high cis polybutadiene having 40% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass or more of cis-1,4-bonds advantageous for repulsion is particularly preferable. The content of polybutadiene in the (a) base material rubber is preferably 70% by mass or more, more preferably 90% by mass or more.

The content of 1,2-vinyl bond in the high cis polybutadiene is preferably 2% by mass or less, more preferably 1.7% by mass or less, still more preferably 1.5% by mass or less. If the content of the 1,2-vinyl bond is too high, the resilience may decrease.

The high cis polybutadiene is preferably synthesized with a rare earth element-based catalyst, and in particular, the use of a neodymium-based catalyst using a neodymium compound which is a lanthanum-series rare earth element compound has a high content of 1,4-cis bonds. , 1,2-vinyl bond is preferable because a polybutadiene rubber having a low content can be obtained with excellent polymerization activity.

The high cis polybutadiene has a Mooney viscosity (ML _{1 + 4} (100 ° C.)) of preferably 30 or more, more preferably 32 or more, still more preferably 35 or more, preferably 140 or less, and more preferably. It is 120 or less, more preferably 100 or less, and most preferably 80 or less. The Mooney viscosity (ML _{1 + 4} (100 ° C.)) in the present invention is based on JIS K6300, using an L rotor, with a preheating time of 1 minute, a rotor rotation time of 4 minutes, and 100 ° C. It is a value measured below.

The high cis polybutadiene has a molecular weight distribution Mw / Mn (Mw: weight average molecular weight, Mn: number average molecular weight) of preferably 2.0 or more, more preferably 2.2 or more, still more preferably 2. It is 4 or more, most preferably 2.6 or more, preferably 6.0 or less, more preferably 5.0 or less, still more preferably 4.0 or less, and most preferably 3.4 or less. If the molecular weight distribution (Mw / Mn) of high cis polybutadiene is too small, workability may decrease, and if it is too large, resilience may decrease. The molecular weight distribution was determined by gel permeation chromatography (manufactured by Tosoh Corporation, "HLC-8120GPC") using a differential refractometer as a detector, column: GMHHXL (manufactured by Tosoh Corporation), column temperature: 40 ° C., mobile phase. : It is a value calculated under the condition of tetrahydrofuran and calculated as a standard polystyrene conversion value.

(B) Co-crosslinking agent The (b) α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or a metal salt thereof is blended in a rubber composition as a co-crosslinking agent. By graft-polymerizing the base rubber molecular chain, it has the effect of cross-linking the rubber molecules. When only the α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms is blended as the cocrosslinking agent, it is preferable to further blend the metal compound (e) described later in the rubber composition. By neutralizing α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms in the rubber composition with a metal compound, α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms as a co-crosslinking agent A substantially similar effect can be obtained as when a metal salt of an acid is used. Even when a metal salt of α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms is blended as the co-crosslinking agent, the metal compound (e) may be used as an optional component.

Examples of the α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms include acrylic acid, methacrylic acid, fumaric acid, maleic acid, and crotonic acid.

Metals constituting the metal salt of α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms include monovalent metal ions such as sodium, potassium and lithium; magnesium, calcium, zinc, barium and cadmium. Divalent metal ions; trivalent metal ions such as aluminum; other ions such as tin and zirconium. The metal component can also be used alone or as a mixture of two or more kinds. Among these, as the metal component, a divalent metal such as magnesium, calcium, zinc, barium, or cadmium is preferable. This is because the use of a divalent metal salt of α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms facilitates metal cross-linking between rubber molecules. In particular, as the divalent metal salt, zinc acrylate is suitable because the resilience of the obtained golf ball is high. The α, β-unsaturated carboxylic acid and / or a metal salt thereof having 3 to 8 carbon atoms may be used alone or in combination of two or more.

(B) The blending amount of α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or a metal salt thereof is preferably 15 parts by mass or more with respect to 100 parts by mass of (a) base material rubber. 20 parts by mass or more is more preferable, 25 parts by mass or more is further preferable, 50 parts by mass or less is more preferable, 45 parts by mass or less is more preferable, and 35 parts by mass or less is further preferable. (B) When the content of the α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or the metal salt thereof is less than 15 parts by mass, the member formed from the rubber composition has an appropriate hardness. In addition, the amount of the (d) cross-linking initiator described later must be increased, and the resilience of the golf ball tends to decrease. On the other hand, when the content of α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or a metal salt thereof exceeds 50 parts by mass, the member formed from the rubber composition becomes too hard, and golf The shot feeling of the ball may be reduced.

(C) Crosslinkable compound having two or more polymerizable unsaturated bonds in the molecule Examples of the polymerizable unsaturated bond possessed by the (c) crosslinkable compound include a carbon-carbon double bond and a carbon-carbon triple bond. A carbon-carbon double bond is preferred. The number of polymerizable unsaturated bonds contained in the molecule of the (c) crosslinkable compound is 2 or more, preferably 6 or less, and more preferably 4 or less. The crosslinkable compound (c) may be used alone or in combination of two or more. The (c) crosslinkable compound does not contain α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and a metal salt thereof, which are used as the (b) co-crosslinking agent.

The molecular weight of the (c) crosslinkable compound is preferably 100 or more, more preferably 130 or more, further preferably 150 or more, preferably 500 or less, more preferably 450 or less, still more preferably 400 or less.

As the (c) crosslinkable compound, a crosslinkable compound having two or more vinyl groups in the molecule is preferable, and a crosslinkable compound having two or more (meth) acryloyl groups in the molecule is more preferable. In addition, "(meth) acryloyl group" represents "acryloyl group and / or methacryloyl group".

Examples of the crosslinkable compound having two or more vinyl groups in the molecule include divinylbenzene, trivinylbenzene, divinylnaphthalene, trivinylnaphthalene, divinylanthracene, trivinylanthracene, divinylcyclohexane, and trivinylcyclohexane.

Examples of the crosslinkable compound having two or more (meth) acryloyl groups in the molecule include esters of divalent to hexavalent alcohols and (meth) acrylic acid. In addition, "(meth) acrylic acid" represents "acrylic acid and / or methacrylic acid". Examples of the divalent to hexavalent alcohol include alkane polyols having 2 to 20 carbon atoms, and alkane diols having 2 to 20 carbon atoms and alkane triol having 2 to 20 carbon atoms are preferable.

Examples of the crosslinkable compound having two or more (meth) acryloyl groups in the molecule include ethylene glycol di (meth) acrylate, propanediol di (meth) acrylate, butanediol di (meth) acrylate, and pentanediol di (meth). Crosslinkable compounds having two (meth) acryloyl groups in the molecule, such as acrylates, hexanediol di (meth) acrylates, heptanediol di (meth) acrylates, octanediol di (meth) acrylates; trimethylolpropanetri (meth). Examples thereof include crosslinkable compounds having three (meth) acryloyl groups in the molecule such as acrylate and pentaerythritol tri (meth) acrylate. Among these, the crosslinkable compound (c) is selected from the group consisting of trimethylolpropane tri (meth) acrylate, ethylene glycol di (meth) acrylate, and 1,6-hexanediol di (meth) acrylate. At least one is preferred.

The thermal homopolymerization temperature (Tc) of the (c) crosslinkable compound is preferably 120 ° C. or higher, more preferably 130 ° C. or higher, still more preferably 140 ° C. or higher. If the homopolymerization temperature (Tc) due to the heat of the (c) crosslinkable compound is 120 ° C. or higher, the homopolymerization due to the heat of the (c) crosslinkable compound during press molding of the core can be suppressed, and the inside of the obtained spherical core It becomes easy to form a three-dimensional crosslinked structure. The upper limit of the homopolymerization temperature of the (c) crosslinkable compound by heat is not particularly limited, but is about 300 ° C.

The blending amount of the (c) crosslinkable compound is preferably 2 parts by mass or more, more preferably 3 parts by mass or more, and further preferably 5 parts by mass or more with respect to 100 parts by mass of the (a) base material rubber. , 39 parts by mass or less, more preferably 30 parts by mass or less, still more preferably 20 parts by mass or less. When the blending amount of the (c) crosslinkable compound is 2 parts by mass or more, the effect of improving the durability of the golf ball is improved, and when it is 39 parts by mass or less, the deterioration of the repulsive performance of the golf ball can be further reduced.

(D) Crosslinking Initiator The above-mentioned (d) Crosslinking Initiator is formulated to crosslink (a) the base rubber component. (D) Organic peroxides are suitable as the cross-linking initiator. Specific examples of the organic peroxide include dialkyl peroxides, peroxyesters, peroxyketals, and hydroperoxides. Examples of the dialkyl peroxide include di (2-t-butylperoxyisopropyl) benzene (175.4 ° C), dicumyl peroxide (175.2 ° C), and 2,5-dimethyl-2,5-di (t). -Butylperoxy) Hexane (179.8 ° C), t-Butylcumylperoxy (173.3 ° C), Di-t-hexylperoxy (176.7 ° C), Di-t-butylperoxy (185.9 ° C) , 2,5-Dimethyl-2,5-di (t-butylperoxy) hexin-3 (194.3 ° C.) and the like. Examples of the peroxyester include t-butylperoxymaleate (167.5 ° C.), t-butylperoxy-3,3,5-trimethylcyclohexanoate (166.0 ° C.), and t-butylperoxylaurate (166.0 ° C.). 159.4 ° C), t-butylperoxyisopropyl monocarbonate (158.8 ° C), t-hexylperoxybenzoate (160.3 ° C), 2,5-dimethyl-2,5-di (benzoylperoxy) hexane (158 ° C). .2 ° C), t-butylperoxyacetate (159.9 ° C), t-butylperoxybenzoate (166.8 ° C) and the like. Examples of the peroxyketal include 1,1-di (t-hexylperoxy) -3,3,5-trimethylcyclohexane (147.1 ° C.) and 1,1-di (t-hexylperoxy) cyclohexane (149. 2 ° C), 1,1-di (t-butylperoxy) -2-methylcyclohexane (142.1 ° C), 1,1-di (t-butylperoxy) cyclohexane (153.8 ° C), 2,2- Di (t-butylperoxy) butane (159.9 ° C), n-butyl-4,4-di (t-butylperoxy) valerate (172.5 ° C), 2,2-di (4,4-di (4,4-di) Examples thereof include t-butylperoxy) cyclohexyl) propane (153.8 ° C.). Examples of the hydroperoxide include p-menthane hydroperoxide (199.5 ° C.) and diisopropylbenzene hydroperoxide (232.5 ° C.). The numerical values described in parentheses after the compound name of the organic peroxide are these 1-minute half-life temperatures. These organic peroxides may be used alone or in combination of two or more. When two or more of the above organic peroxides are used in combination, the difference between the maximum value and the minimum value of the 1-minute half-life temperature of the organic peroxide used is preferably 25 ° C. or less, more preferably 10 ° C. or less. Is.

The 1-minute half-life temperature (Td) of the (d) cross-linking initiator is preferably less than 160 ° C, more preferably 158 ° C or lower, still more preferably 155 ° C or lower. (D) If the 1-minute half-life temperature of the cross-linking initiator is less than 160 ° C., the molding temperature of the spherical core can be set low, and deterioration of the base rubber can be suppressed. The 1-minute half-life temperature of the (d) cross-linking initiator is preferably 100 ° C. or higher, more preferably 105 ° C. or higher, and even more preferably 110 ° C. or higher. (D) When the 1-minute half-life temperature of the cross-linking initiator is 100 ° C. or higher, decomposition of the (d) cross-linking initiator can be suppressed when preparing the rubber composition.

The blending amount of the (d) cross-linking initiator is preferably 0.1 part by mass or more, more preferably 0.5 part by mass or more, still more preferably 0.7 with respect to 100 parts by mass of the (a) base material rubber. It is more than parts by mass, preferably 5.0 parts by mass or less, more preferably 2.5 parts by mass or less, still more preferably 2.0 parts by mass or less. If it is less than 0.1 part by mass, the member formed from the rubber composition tends to be too soft and the resilience of the golf ball tends to decrease, and if it exceeds 5.0 parts by mass, it is formed from the rubber composition. In order to make the member have an appropriate hardness, it is necessary to reduce the amount of the above-mentioned (b) co-crosslinking agent used, which may result in insufficient resilience of the golf ball or deterioration of durability.

(E) Metal compound When only α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms is blended as the co-crosslinking agent, it is preferable to further blend (e) the metal compound in the rubber composition for the core. .. The metal compound (e) is not particularly limited as long as it can neutralize (b) an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms in the rubber composition. Examples of the metal compound (e) include metal hydroxides such as magnesium hydroxide, zinc hydroxide, calcium hydroxide, sodium hydroxide, lithium hydroxide, potassium hydroxide and copper hydroxide; magnesium oxide and calcium oxide. , Metal oxides such as zinc oxide and copper oxide; metal carbon oxides such as magnesium carbonate, zinc carbonate, calcium carbonate, sodium carbonate, lithium carbonate and potassium carbonate. The metal compound (e) is preferably a divalent metal compound, and more preferably a zinc compound. This is because the divalent metal compound reacts with an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms to form a metal crosslink. Further, by using a zinc compound, a golf ball having high resilience can be obtained. (E) The metal compound may be used alone or in combination of two or more. The content of the (e) metal compound may be appropriately adjusted according to the desired degree of neutralization of the desired (b) α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms.

(F) Organic Sulfur Compound The core rubber composition may further contain (f) an organic sulfur compound. When the rubber composition contains (f) an organic sulfur compound, the resilience of the spherical core is further improved. The organic sulfur compound (f) can be used alone or in combination of two or more.

The organic sulfur compound (f) is not particularly limited as long as it is an organic compound having a sulfur atom in the molecule, and is, for example, a thiol group (-SH) or a polysulfide bond having 2 to 4 sulfur numbers (-). Organic compounds having S-S-, -S-S-S-, or -S-S-S-S-), or metal salts thereof (-SM, -S-M-S-, -S-). M-S-S-, -S-S-M-S-S-, -S-M-S-S-S-, etc., where M is a metal atom) can be mentioned. Examples of the metal salt include monovalent metal salts such as sodium, lithium, potassium, copper (I) and silver (I), zinc, magnesium, calcium, strontium, barium, titanium (II) and manganese (II). Examples thereof include divalent metal salts such as iron (II), cobalt (II), nickel (II), zirconium (II) and tin (II). The organic sulfur compound (f) includes an aliphatic compound (aliphatic thiol, an aliphatic thiocarboxylic acid, an aliphatic dithiocarboxylic acid, an aliphatic polysulfide, etc.), a heterocyclic compound, and an alicyclic compound (alicyclic thiol, alicyclic thiol, etc.). It may be any of an alicyclic thiocarboxylic acid, an alicyclic dithiocarboxylic acid, an alicyclic polysulfide, etc.) and an aromatic compound.

Examples of the (f) organic sulfur compound include thiols (thiophenols, thionaphthols), polysulfides, thiurams, thiocarboxylic acids, dithiocarboxylic acids, sulfenamides, dithiocarbamates, thiazoles and the like. Can be mentioned.

Examples of thiols include thiophenols and thionaphthols. Examples of the thiophenols include thiophenol; 4-fluorothiophenol, 2,5-difluorothiophenol, 2,6-difluorothiophenol, 2,4,5-trifluorothiophenol, 2,4,5. , 6-Tetrafluorothiophenol, pentafluorothiophenol and other fluorogroup-substituted thiophenols; 2-chlorothiophenol, 4-chlorothiophenol, 2,4-dichlorothiophenol, 2,5-dichlorothiophenol Phenols substituted with chloro groups such as phenol, 2,6-dichlorothiophenol, 2,4,5-trichlorothiophenol, 2,4,5,6-tetrachlorothiophenol, pentachlorothiophenol; 4 -Bromothiophenol, 2,5-dibromothiophenol, 2,6-dibromothiophenol, 2,4,5-tribromothiophenol, 2,4,5,6-tetrabromothiophenol, pentabromothiophenol, etc. Thiophenols substituted with the bromo group of; 4-iodothiophenol, 2,5-diiodothiophenol, 2,6-diiodothiophenol, 2,4,5-triiodothiophenol, 2,4. Thiophenols substituted with iodo groups such as 5,6-tetraiodothiophenol, pentaiodothiophenol; or metal salts thereof. As the metal salt, a zinc salt is preferable.

Examples of the thionaphthols (naphtholenethiols) include 2-thionaphthol, 1-thionaphthol, 1-chloro-2-thionaphthol, 2-chloro-1-thionaphthol, 1-bromo-2-thionaphthol, 2 -Bromo-1-thionaphthol, 1-fluoro-2-thionaphthol, 2-fluoro-1-thionaphthol, 1-cyano-2-thionaphthol, 2-cyano-1-thionaphthol, 1-acetyl-2- Thionaphthol, 2-acetyl-1-thionaphthol, or metal salts thereof can be mentioned, with 2-thionaphthol, 1-thionaphthol, or metal salts thereof being preferred. The metal salt is preferably a divalent metal salt, more preferably a zinc salt. Specific examples of the metal salt include a zinc salt of 1-thionaphthol and a zinc salt of 2-thionaphthol.

The polysulfides are organic sulfur compounds having a polysulfide bond, and examples thereof include disulfides, trisulfides, and tetrasulfides. As the polysulfides, diphenyl polysulfides are preferable.

Examples of diphenyl polysulfides include diphenyl disulfides; bis (4-fluorophenyl) disulfides, bis (2,5-difluorophenyl) disulfides, bis (2,6-difluorophenyl) disulfides, and bis (2,4,5-). Trifluorophenyl) disulfide, bis (2,4,5,6-tetrafluorophenyl) disulfide, bis (pentafluorophenyl) disulfide, bis (4-chlorophenyl) disulfide, bis (2,5-dichlorophenyl) disulfide, bis ( 2,6-dichlorophenyl) disulfide, bis (2,4,5-trichlorophenyl) disulfide, bis (2,4,5,6-tetrachlorophenyl) disulfide, bis (pentachlorophenyl) disulfide, bis (4-bromophenyl) Disulfide, bis (2,5-dibromophenyl) disulfide, bis (2,6-dibromophenyl) disulfide, bis (2,4,5-tribromophenyl) disulfide, bis (2,4,5,6-tetrabromo) Phenyl) disulfide, bis (pentabromophenyl) disulfide, bis (4-iodophenyl) disulfide, bis (2,5-diiodophenyl) disulfide, bis (2,6-diiodophenyl) disulfide, bis (2,4) , 5-Triiodophenyl) Disulfides substituted with halogen groups such as disulfides, bis (2,4,5,6-tetraiodophenyl) disulfides, bis (pentaiodophenyl) disulfides; bis (4-methylphenyl) ) Disulfide, bis (2,4,5-trimethylphenyl) disulfide, bis (pentamethylphenyl) disulfide, bis (4-t-butylphenyl) disulfide, bis (2,4,5-tri-t-butylphenyl) Examples thereof include diphenyl disulfides substituted with an alkyl group such as disulfide and bis (penta-t-butylphenyl) disulfide.

Examples of thiurams include thiuram monosulfides such as tetramethylthium monosulfide, thiuram disulfides such as tetramethylthium disulfide, tetraethyl thiuram disulfide, and tetrabutyl thiuram disulfide, and thiuram tetrasulfides such as dipentamethylene thiuram tetrasulfide. Can be mentioned. Examples of the thiocarboxylic acids include naphthalene thiocarboxylic acids. Examples of the dithiocarboxylic acids include naphthalene dithiocarboxylic acids. Examples of sulfenamides include N-cyclohexyl-2-benzothiazolesulfenamide, N-oxydiethylene-2-benzothiazolesulfenamide, and Nt-butyl-2-benzothiazolesulfenamide. Can be mentioned.

(F) As the organic sulfur compound, thiophenols and / or metal salts thereof, thionaphthols and / or metal salts thereof, diphenyldisulfides and thiuram disulfides are preferable, and 2,4-dichlorothiophenol, more preferably. 2,6-difluorothiophenol, 2,6-dichlorothiophenol, 2,6-dibromothiophenol, 2,6-diiodothiophenol, 2,4,5-trichlorothiophenol, pentachlorothiophenol, 1- Thionaphthol, 2-thionaphthol, diphenyl disulfide, bis (2,6-difluorophenyl) disulfide, bis (2,6-dichlorophenyl) disulfide, bis (2,6-dibromophenyl) disulfide, bis (2,6-di) Iodophenyl) disulfide and bis (pentabromophenyl) disulfide.

The content of (f) the organic sulfur compound is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and 5.0 parts by mass with respect to 100 parts by mass of the (a) base material rubber. It is preferably 2 parts or less, more preferably 2.0 parts by mass or less. If it is less than 0.05 parts by mass, the effect of adding the (f) organic sulfur compound cannot be obtained, and the resilience of the golf ball may not be improved. On the other hand, if it exceeds 5.0 parts by mass, the amount of compression deformation of the obtained golf ball may increase and the resilience may decrease.

(G) Carboxylic acid and / or a metal salt thereof The rubber composition for a core may further contain (g) a carboxylic acid and / or a metal salt thereof. The (g) carboxylic acid and / or its salt does not include the α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and its metal salt used as the (b) co-crosslinking agent. Examples of the (g) carboxylic acid and / or a salt thereof include saturated fatty acids, saturated fatty acid metal salts, aromatic carboxylic acids and aromatic carboxylic acid metal salts. The (g) carboxylic acid and / or a metal salt thereof can also be used alone or as a mixture of two or more kinds.

Examples of the saturated fatty acid include butanoic acid, pentanoic acid, hexanoic acid, heptanic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid and octadecanoic acid. , Nonadecanic acid, Icosanoic acid, Henicosanoic acid, Docosanoic acid, Tricosanoic acid, Tetracosanoic acid, Pentacosanoic acid, Hexacosanoic acid, Heptacosanoic acid, Octacosanoic acid, Nonacosanoic acid, Triacanthanoic acid and the like.

Examples of the aromatic carboxylic acid include benzoic acid, butyl benzoic acid, anisic acid (methoxybenzoic acid), dimethoxybenzoic acid, trimethoxybenzoic acid, dimethylaminobenzoic acid, chlorobenzoic acid, dichlorobenzoic acid, trichlorobenzoic acid, and acetoxybenzoic acid. Examples thereof include acid, biphenylcarboxylic acid, naphthalenecarboxylic acid and anthracenecarboxylic acid.

Examples of the cationic component of the (g) carboxylate metal salt include monovalent metal ions such as sodium, potassium, lithium and silver; magnesium, calcium, zinc, barium, cadmium, copper, cobalt, nickel and manganese. Divalent metal ions; trivalent metal ions such as aluminum and iron; other ions such as tin, zirconium and titanium. As the (g) carboxylic acid metal salt, a zinc salt of carboxylic acid is preferable. The cationic component can also be used alone or as a mixture of two or more kinds.

If necessary, the rubber composition for a core may contain additives such as pigments, fillers for weight adjustment, antiaging agents, deliquescent agents, and softeners. Further, the rubber composition for a core may contain a core of a golf ball or a rubber powder obtained by crushing scraps generated during core production.

Examples of the pigment blended in the rubber composition include a white pigment, a blue pigment, and a purple pigment. It is preferable to use titanium oxide as the white pigment. The type of titanium oxide is not particularly limited, but it is preferable to use the rutile type because of its good concealing property. The content of titanium oxide is preferably 0.5 parts by mass or more, more preferably 2 parts by mass or more, and more preferably 8 parts by mass or less, based on (a) 100 parts by mass of the base rubber. It is preferably 5 parts by mass or less.

It is also a preferred embodiment that the rubber composition contains a white pigment and a blue pigment. The blue pigment is blended to make the white color look vivid, and examples thereof include ultramarine blue, cobalt blue, and phthalocyanine blue. Examples of the purple pigment include anthraquinone violet, dioxazine violet, and methyl violet.

The filler used in the rubber composition is mainly blended as a weight adjusting agent for adjusting the weight of a golf ball obtained as a final product, and may be blended as necessary. Examples of the filler include inorganic fillers such as barium sulfate, calcium carbonate, magnesium oxide, tungsten powder, and molybdenum powder.

The content of the antiaging agent is preferably 0.1 part by mass or more and 1 part by mass or less with respect to 100 parts by mass of (a) base material rubber. The content of the deliquescent agent is preferably 0.1 part by mass or more and 5 parts by mass or less with respect to 100 parts by mass of (a) base rubber.

(2) Second Step In the second step, a spherical core is formed from the rubber composition for a core. The rubber composition for a core obtained by kneading is extruded into a rod shape by an extruder and cut to a predetermined length to prepare a preformed body (also referred to as “plug”). When an extruder is used to manufacture the plug, the rubber composition may be heated during kneading, but the heating temperature is preferably 75 ° C. or lower. Further, the rubber composition for a core may be formed into a thick sheet and punched out to form a plug. The size of the plug may be appropriately changed according to the size of the compression molding die. It is preferable that the obtained plugs are, for example, immersed in an adhesive solution so as not to stick to each other, dried, and then aged for about 8 to 48 hours.

Next, the plug is put into a core molding die and press-molded. In the production method of the present invention, the molding temperature (T2) is set to 100 ° C. to 150 ° C. in the step of heating and pressing the rubber composition to form the spherical core. By setting the heating press temperature in this range, (c) homopolymerization of the crosslinkable compound due to heat can be suppressed. The molding temperature is preferably 110 ° C. or higher, more preferably 120 ° C. or higher, preferably 145 ° C. or lower, and more preferably 140 ° C. or lower. In the present invention, the press temperature is a set temperature of the press molding machine.

The temperature difference (Tc—T2) between the molding temperature (T2) and the homopolymerization temperature (Tc) due to the heat of the (c) crosslinkable compound is preferably 1 ° C. or higher, more preferably 5 ° C. or higher, still more preferably. It is 10 ° C. or higher. When the temperature difference (Tc-T2) is 1 ° C. or higher, (c) homopolymerization of the crosslinkable compound due to heat is suppressed. The upper limit of the temperature difference (Tc-T2) is not particularly limited, but is about 200 ° C. When two or more kinds of the component (c) are used as the compounding material, it is preferable that the above range is satisfied for all the components (c).

The temperature difference (Td—T2) between the molding temperature (T2) and the 1-minute half-life temperature (Td) of the (d) crosslinking initiator is preferably 40 ° C. or lower, more preferably 35 ° C. or lower. More preferably, it is 30 ° C. or lower. When the temperature difference (Td-T2) is 40 ° C. or less, (d) the cross-linking initiator can be sufficiently decomposed at the molding temperature, and the degree of the outer rigid inner flexible structure of the obtained spherical core becomes large. The temperature difference (Td—T2) is preferably 0 ° C. or higher, more preferably 5 ° C. or higher, and even more preferably 10 ° C. or higher. If the temperature difference (Td—T2) is 0 ° C. or higher, the reaction can be controlled. When two or more kinds of the component (d) are used as the compounding material, it is preferable that the above range is satisfied for all the components (d).

The molding time is preferably 10 minutes or more, more preferably 12 minutes or more, further preferably 15 minutes or more, preferably 60 minutes or less, more preferably 50 minutes or less, still more preferably 45 minutes or less. The pressure during molding is preferably 2.9 MPa to 11.8 MPa.

The spherical core produced in the second step preferably has the following diameter, compressive deformation amount, and hardness.

The diameter of the spherical core is preferably 34.8 mm or more, more preferably 36.8 mm or more, further preferably 38.8 mm or more, preferably 42.2 mm or less, more preferably 41.8 mm or less, still more preferably. It is 41.2 mm or less, and most preferably 40.8 mm or less. When the diameter of the spherical core is 34.8 mm or more, the thickness of the cover does not become too thick, and the resilience becomes better. On the other hand, when the diameter of the spherical core is 42.2 mm or less, the cover does not become too thin and the function of the cover is more exhibited.

When the diameter of the spherical core is 34.8 mm to 42.2 mm, the amount of compression deformation (the amount at which the center shrinks in the compression direction) from the state where the initial load of 98 N is applied to the time when the final load of 1275 N is applied is 1.90 mm. The above is preferable, more preferably 2.00 mm or more, further preferably 2.10 mm or more, preferably 5.00 mm or less, still more preferably 4.80 mm or less, still more preferably 4.60 mm or less. When the amount of compression deformation is 1.90 mm or more, the shot feeling is better, and when it is 5.00 mm or less, the resilience is better.

The spherical core has a hardness difference (Hs-Ho) between the surface hardness Hs and the center hardness Ho, which is preferably 10 or more, more preferably 18 or more, still more preferably 20 or more, and 50 or less in terms of shore D hardness. It is preferable, more preferably 48 or less, still more preferably 45 or less. When the hardness difference between the core surface and the core center is large, a golf ball having a high launch angle and a low spin distance can be obtained.

The center hardness Ho of the spherical core is the shore D hardness, preferably 40 or more, more preferably 45 or more, and further preferably 50 or more. If the center hardness Ho of the spherical core is less than 40 in the shore D hardness, it may become too soft and the resilience may decrease. The central hardness Ho of the spherical core is preferably 65 or less, more preferably 63 or less, and further preferably 60 or less in terms of shore D hardness. This is because when the center hardness Ho exceeds 65 in the shore D hardness, the hardness tends to be too hard and the shot feeling tends to be deteriorated.

The surface hardness Hs of the spherical core is the shore D hardness, preferably 70 or more, more preferably 75 or more, preferably 90 or less, and more preferably 85 or less. By setting the surface hardness of the spherical core to 70 or more in shore D hardness, the spherical core does not become too soft and good resilience can be obtained. Further, by setting the surface hardness of the spherical core to 90 or less in shore D hardness, the spherical core does not become too hard and a good shot feeling can be obtained.

(3) Third Step In the third step, at least one cover covering the spherical core is formed on the spherical core. As a method for molding the cover, for example, a hollow shell-shaped shell is formed from a cover composition containing a resin component, the core is covered with a plurality of shells, and compression molding is performed (preferably, the cover composition). A method of molding a hollow shell-shaped half shell from the above and covering the core with two half shells for compression molding), or a method of directly injection molding a cover composition containing a resin component onto the core. be able to.

Examples of the resin component contained in the cover composition include ionomer resin, a thermoplastic polyurethane elastomer marketed under the trade name "Elastoran (registered trademark)" from BASF Japan Co., Ltd., and a trade name from Alchema Co., Ltd. Thermoplastic polyamide elastomer marketed under "Pevax (registered trademark)", thermoplastic polyester elastomer marketed under the trade name "Hytrel (registered trademark)" from Toray DuPont Co., Ltd., product from Mitsubishi Chemical Co., Ltd. Examples thereof include thermoplastic styrene elastomers commercially available under the name “Lavalon (registered trademark)”.

The ionomer resin is, for example, an olefin in which at least a part of the carboxyl group in the binary copolymer of an olefin and an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms is neutralized with a metal ion. At least a part of the carboxyl group of the ternary copolymer of α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and α, β-unsaturated carboxylic acid ester is neutralized with metal ions, or , These mixtures can be mentioned. As the olefin, an olefin having 2 to 8 carbon atoms is preferable, and examples thereof include ethylene, propylene, butene, pentene, hexene, heptene, and octene, and ethylene is particularly preferable. Examples of the α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms include acrylic acid, methacrylic acid, fumaric acid, maleic acid, crotonic acid and the like, and acrylic acid or methacrylic acid is particularly preferable. As the α, β-unsaturated carboxylic acid ester, for example, methyl, ethyl, propyl, n-butyl, isobutyl ester such as acrylic acid, methacrylic acid, fumaric acid, maleic acid and the like are used, and in particular, acrylic acid ester. Alternatively, a methacrylic acid ester is preferable. Among these, the ionomer resin includes a metal ion neutralized product of an ethylene- (meth) acrylic acid binary copolymer and a ternary copolymer of ethylene- (meth) acrylic acid- (meth) acrylic acid ester. Metal ion neutralized products are preferred.

To exemplify a specific example of the ionomer resin by a trade name, "Himilan® (registered trademark)" commercially available from Mitsui Dupont Polychemical Co., Ltd. (for example, Himilan 1555 (Na), 1557 (Zn), 1605 (Na), 1706 (Zn), 1707 (Na), AM3711 (Mg) and the like can be mentioned, and examples of the ternary copolymer ionomer resin include Hymilan 1856 (Na), 1855 (Zn) and the like). ..

Further, as an ionomer resin commercially available from DuPont, "Surlyn (registered trademark) (for example, Sarlin 8945 (Na), 9945 (Zn), 8140 (Na), 8150 (Na), 9120 (Zn)) , 9150 (Zn), 6910 (Mg), 6120 (Mg), 7930 (Li), 7940 (Li), AD8546 (Li) and the like, and examples of the ternary copolymer ionomer resin include surrin 8120 (Na). , 8320 (Na), 9320 (Zn), 6320 (Mg), HPF1000 (Mg), HPF2000 (Mg), etc.) ”.

Examples of the ionomer resin commercially available from Exxon Mobile Chemical Co., Ltd. include "Iotech® (registered trademark) (for example, Iotech 8000 (Na), 8030 (Na), 7010 (Zn), 7030 (Zn), etc." As the ternary copolymer ionomer resin, Iotech 7510 (Zn), 7520 (Zn), etc.) ”.

In addition, Na, Zn, Li, Mg and the like described in parentheses after the trade name of the ionomer resin indicate the metal species of these neutralized metal ions. The ionomer resin may be used alone or in combination of two or more.

The cover composition constituting the cover of the golf ball of the present invention preferably contains a thermoplastic polyurethane elastomer or an ionomer resin as a resin component. When an ionomer resin is used, it is also preferable to use a thermoplastic styrene elastomer in combination. The content of the polyurethane or ionomer resin in the resin component of the cover composition is preferably 50% by mass or more, more preferably 60% by mass or more, still more preferably 70% by mass or more.

In addition to the above-mentioned resin components, the cover composition includes pigment components such as white pigments (for example, titanium oxide), blue pigments and red pigments, weight modifiers such as zinc oxide, calcium carbonate and barium sulfate, and dispersants. An antiaging agent, an ultraviolet absorber, a light stabilizer, a fluorescent material, a fluorescent whitening agent, or the like may be contained within a range that does not impair the performance of the cover.

The content of the white pigment (for example, titanium oxide) is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and 10 parts by mass with respect to 100 parts by mass of the resin component constituting the cover. The following is preferable, and more preferably 8 parts by mass or less. By setting the content of the white pigment to 0.5 parts by mass or more, the cover can be concealed. Further, when the content of the white pigment exceeds 10 parts by mass, the durability of the obtained cover may decrease.

As a method for molding the cover, for example, a hollow shell-shaped shell is formed from the cover composition, the core is covered with a plurality of shells, and compression molding is performed (preferably, the hollow shell-shaped shell is formed from the cover composition. A method of molding the half shell of the above and covering the core with two half shells and compression molding), or a method of injection molding the cover composition directly onto the core can be mentioned.

When the cover is molded by a compression molding method, the half shell can be molded by either a compression molding method or an injection molding method, but the compression molding method is preferable. The conditions for compression molding the cover composition into a half shell include, for example, a pressure of 1 MPa or more and 20 MPa or less, and −20 ° C. or higher and 70 ° C. or lower with respect to the flow start temperature of the cover composition. The molding temperature can be mentioned. By setting the molding conditions, a half shell having a uniform thickness can be molded. As a method of molding the cover using the half shell, for example, a method of covering the core with two half shells and compression molding can be mentioned. The conditions for compression molding the half shell to form the cover are, for example, a molding pressure of 0.5 MPa or more and 25 MPa or less, and −20 ° C. or higher and 70 ° C. or lower with respect to the flow start temperature of the cover composition. The molding temperature can be mentioned. By setting the molding conditions, a golf ball cover having a uniform cover thickness can be molded.

When the cover composition is injection-molded to form a cover, the pellet-shaped cover composition obtained by extrusion may be used for injection molding, or for a cover such as a base resin component or a pigment. The materials may be dry blended and directly injection molded. As the upper and lower molds for cover molding, it is preferable to use a mold having a hemispherical cavity, with pimples, and a part of the pimples also serving as a hold pin that can move forward and backward. In the molding of the cover by injection molding, the cover can be molded by sticking out the hold pin, inserting the core and holding the cover, then injecting the composition for the cover and cooling, for example, 9 MPa to 15 MPa. The cover composition heated to 200 ° C. to 250 ° C. is injected into a pressure-molded mold in 0.5 seconds to 5 seconds, cooled for 10 seconds to 60 seconds, and opened.

When molding a cover, dents called dimples are usually formed on the surface. The total number of dimples formed on the cover is preferably 200 or more and 500 or less. If the total number of dimples is less than 200, it is difficult to obtain the effect of dimples. Further, when the total number of dimples exceeds 500, the size of each dimple becomes small, and it is difficult to obtain the effect of the dimples. The shape of the dimples to be formed (planar shape) is not particularly limited, and a circle; a polygon such as a substantially triangle, a substantially quadrangle, a substantially pentagon, and a substantially hexagon; and other indefinite shapes; are used alone. Alternatively, two or more kinds may be used in combination.

The thickness of the cover is preferably 4.0 mm or less, more preferably 3.0 mm or less, still more preferably 2.0 mm or less. When the thickness of the cover is 4.0 mm or less, the resilience and shot feeling of the obtained golf ball become better. The thickness of the cover is preferably 0.3 mm or more, more preferably 0.5 mm or more, still more preferably 0.8 mm or more, and particularly preferably 1.0 mm or more. If the thickness of the cover is less than 0.3 mm, the durability and wear resistance of the cover may decrease. In the case of a plurality of cover layers, it is preferable that the total thickness of the plurality of cover layers is in the above range.

It is preferable that the golf ball body on which the cover is formed is taken out from the mold and, if necessary, surface-treated such as deburring, cleaning, and sandblasting. Further, if desired, a coating film or a mark can be formed. The film thickness of the coating film is not particularly limited, but is preferably 5 μm or more, more preferably 7 μm or more, more preferably 50 μm or less, still more preferably 40 μm or less, still more preferably 30 μm or less. This is because if the film thickness is less than 5 μm, the coating film is likely to wear away due to continuous use, and if the film thickness exceeds 50 μm, the effect of dimples is reduced and the flight performance of the golf ball is deteriorated.

[Golf ball]
The structure of the golf ball produced by the production method of the present invention is not particularly limited as long as it has a spherical core and one or more covers covering the spherical core. The spherical core preferably has a single-layer structure. This is because the spherical core having a single-layer structure has no energy loss at the interface of the multi-layer structure and has improved resilience. Further, the cover may have a structure of one or more layers, and may have a single-layer structure or a multi-layer structure of at least two or more layers. The golf ball includes, for example, a two-piece golf ball including a spherical core and a single-layer cover arranged so as to cover the spherical core; two arranged so as to cover the spherical core and the spherical core. Multi-piece golf balls with more than one layer of cover (including three-piece golf balls); a spherical core, a thread rubber layer provided around the spherical core, and a cover disposed to cover the thread rubber layer. A thread-wound golf ball having the above can be mentioned. The present invention can be suitably used for a golf ball having any of the above structures.

The diameter of the golf ball is preferably 40 mm to 45 mm. A diameter of 42.67 mm or more is particularly preferred from the perspective of meeting the standards of the United States Golf Association (USGA). From the viewpoint of suppressing air resistance, the diameter is more preferably 44 mm or less, and particularly preferably 42.80 mm or less. The mass of the golf ball is preferably 40 g or more and 50 g or less. From the viewpoint of obtaining a large inertia, the mass is more preferably 44 g or more, and particularly preferably 45.00 g or more. From the viewpoint that the USGA standard is satisfied, the mass is particularly preferably 45.93 g or less.

When the diameter of the golf ball is 40 mm to 45 mm, the amount of compression deformation (amount of shrinkage in the compression direction) when the final load of 1275N is applied from the state where the initial load of 98N is applied is preferably 2.0 mm or more. It is more preferably 2.2 mm or more, further preferably 2.4 mm or more, preferably 4.0 mm or less, more preferably 3.5 mm or less, still more preferably 3.4 mm or less. A golf ball having a compression deformation amount of 2.0 mm or more does not become too hard and has a good shot feeling. On the other hand, by setting the amount of compression deformation to 4.0 mm or less, the resilience becomes high.

The golf ball of the present invention is characterized in that it is manufactured by the above-mentioned manufacturing method. That is, the golf ball of the present invention is a golf ball having a spherical core and at least one layer or more of a cover covering the spherical core, wherein the spherical core is (a) a base material rubber and (b) a co-crosslinking agent. Α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or a metal salt thereof, (c) a crosslinkable compound having two or more polymerizable unsaturated bonds in the molecule, (d) a crosslink initiator. It is produced by heat-pressing a rubber composition containing the above, and is characterized in that the temperature of the heating press is 100 ° C. to 150 ° C.

FIG. 1 is a partially cutaway sectional view showing a golf ball 1 according to an embodiment of the present invention. The golf ball 1 has a spherical core 2 and a cover 3 that covers the spherical core 2. A large number of dimples 31 are formed on the surface of this cover. The portion of the surface of the golf ball 3 other than the dimple 31 is the land 32. The golf ball 1 has a paint layer and a mark layer on the outside of the cover 3, but the illustration of these layers is omitted.

Hereinafter, the present invention will be described in detail by way of examples, but the present invention is not limited to the following examples, and changes and embodiments within the scope not deviating from the gist of the present invention are all of the present invention. Included within range.

[Evaluation method]
(1) (c) Thermal polymerization temperature of the crosslinkable compound (c) The thermal polymerization temperature of the crosslinkable compound was measured using a differential scanning calorimeter (DSC). The temperature rise rate was 10 ° C./min and the measurement temperature range was −10 ° C. to 250 ° C. For the obtained DSC curve, the temperature at the peak top was read, and this was taken as the polymerization temperature by heat.

(2) Core hardness (shore D hardness)
The hardness measured on the surface of the core was defined as the core surface hardness. Further, the core was cut into a hemispherical shape, and the hardness measured at the center of the cut surface was defined as the core center hardness. The hardness was measured using an automatic hardness tester (Digitest II, manufactured by H. Burleys). As the detector, "Shore D" was used.

(3) Compressive deformation amount (mm)
The amount of deformation in the compression direction (the amount of shrinkage of the core or golf ball in the compression direction) from the state in which the initial load of 98N was applied to the core or the golf ball to the time when the final load of 1275N was applied was measured.

(4) Driver flight distance A metal head W # 1 driver (Dunlop Sports, XXIO S loft 11 °) is attached to a swing robot M / C manufactured by Golf Laboratory, and a golf ball is hit at a head speed of 40 m / sec. Then, the flight distance (distance from the launch point to the stationary point) was measured. The measurement was performed 12 times for each golf ball, and the average value was taken as the measured value of the golf ball. The flight distance of each golf ball is the golf ball No. It is shown by the difference from the flight distance of 7 (difference in flight distance = flight distance of each golf ball-golf ball golf ball No. 7 flight distance).

(5) Durability Twelve golf balls were collided with a metal plate at a speed of 45 m / sec using an air gun, and the number of repetitions until the golf balls broke was measured. The durability is the golf ball No. The durability of 16 is set to 100, and it is shown as an indexed value.

[Making golf balls]
(1) Preparation of rubber composition for core The compounding materials shown in Tables 1 and 2 were kneaded using a kneader to prepare a mixture. Subsequently, the obtained mixture and the components (c) and (d) were kneaded using a kneading roll so as to have the formulations shown in Tables 1 and 2, to prepare a rubber composition for a core. An appropriate amount of barium sulfate was added so that the mass of the obtained golf ball was 45.4 g.

The materials used in Tables 1 and 2 are as follows.
Polybutadiene rubber: JSR, BR730 (High cis polybutadiene rubber (cis-1,4-bond content = 95% by mass, 1,2-vinyl bond content = 1.3% by mass, Mooney viscosity (ML _{1 + 4)} (100 ° C.)) = 55, molecular weight distribution (Mw / Mn) = 3))
ZN-DA90S: Zinc acrylate (containing 10% by mass of zinc stearate) manufactured by Nikko Techno Fine Chemical Co., Ltd.
Zinc oxide: "Ginmine R" manufactured by Toho Zinc Co., Ltd.
Barium Sulfate: "Barium Sulfate BD" manufactured by Sakai Chemical Industry Co., Ltd.
Perhexa (registered trademark) C-40: NOF Corporation, 1,1-di (t-butylperoxy) cyclohexane Perhexa HC: NOF Corporation, 1,1-di (t-hexylperoxy) cyclohexane park mill (registered trademark) ) D: NOF Corporation, Dikmyl Peroxide TMPT: Shin-Nakamura Chemical Industry Co., Ltd., Trimethylol Propanetrimethacrylate A-TMPT: Shin-Nakamura Chemical Industry Co., Ltd., Trimethylol Propanetriacrylate EGDMA: Tokyo Kasei Kogyo Co., Ltd., Ethylene glycol dimethacrylate HDDMA: manufactured by Tokyo Kasei Kogyo Co., Ltd., 1,6-hexanediol dimethacrylate

(2) Preparation of spherical core The obtained rubber composition for a core was extruded with an extruder to prepare a plug. This plug was put into an upper and lower die having a hemispherical cavity and heated and pressed under the conditions shown in Tables 3 and 4 to obtain a spherical core. The amount of compression deformation and hardness of the obtained spherical core were measured, and the results are shown in Tables 3 and 4.

(3) Cover Molding Using the compounding materials shown in Table 5, mixing was performed with a twin-screw kneading extruder to obtain a pellet-shaped cover composition. The extrusion conditions were a screw diameter of 45 mm, a screw rotation speed of 200 rpm, and a screw L / D = 35, and the compound was heated to 160 ° C. to 230 ° C. at the position of the die of the extruder.

The materials used in Table 5 are as follows.
Hymilan 1605: Mitsui-Dupont Polychemical Co., Ltd., Sodium Ion Neutralized Ethylene-Methacrylic Acid Copolymerization System Ionomer Resin Hymilan 1706: Mitsui-Dupont Polychemical Co., Ltd., Zinc Ion Neutralized Ethylene-Methacrylic Acid Copolymerization System Ionomer Resin Titanium oxide: manufactured by Ishihara Sangyo Co., Ltd., A220

The cover composition obtained above was injection-molded onto the spherical core obtained as described above to form a cover covering the spherical core. The upper and lower molding dies for molding the cover have a hemispherical cavity, have pimples, and also serve as a hold pin on which a part of the pimples can move forward and backward. At the time of cover molding, the hold pin is pushed out, the core is put in and then held, and the resin heated to 210 ° C to 260 ° C is injected into the mold molded with a pressure of 80 tons in 0.3 seconds and cooled for 30 seconds. I opened the mold and took out the golf ball.

After sandblasting the surface of the obtained golf ball body and marking it, clear paint is applied and the paint is dried in an oven at 40 ° C. to obtain a golf ball having a diameter of 42.8 mm and a mass of 45.4 g. rice field. The evaluation results of the obtained golf balls are shown in Tables 3 and 4.

Manufacturing method No. 1 to 13, 17 and 19 are cases where the rubber composition contains (c) a crosslinkable compound and the molding temperature at the time of core molding is 100 ° C to 150 ° C. Golf ball No. obtained by these manufacturing methods. 1 to 13, 17 and 19 are excellent in durability.
Manufacturing method No. 14, 15 and 18 are cases where the rubber composition contains (c) a crosslinkable compound, but the molding temperature at the time of core molding exceeds 150 ° C. Golf ball No. obtained by these manufacturing methods. 14, 15 and 18 are inferior in durability.
Manufacturing method No. 16 and 20 are cases where the rubber composition does not contain (c) a crosslinkable compound. Golf ball No. obtained by this manufacturing method. 16 and 20 are inferior in durability.

1: Golf ball 2: Spherical core 3: Cover, 31: Dimple, 32: Land

Claims (9)

A method for manufacturing a golf ball having a spherical core and at least one layer or more of a cover covering the spherical core.
(A) Base rubber, (b) α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or a metal salt thereof as a co-crosslinking agent, (c) two polymerizable unsaturated bonds in the molecule. The first step of kneading the crosslinkable compound having the above and (d) the crosslinker to prepare a rubber composition for a core, and
The second step of producing a spherical core at a molding temperature (T2) of 100 ° C. to 150 ° C. using the rubber composition for a core, and
It has a third step of forming at least one layer of a cover covering the spherical core on the spherical core.
In the second step, the temperature difference (Tc—T2) between the molding temperature (T2) and the homopolymerization temperature (Tc) due to the heat of the (c) crosslinkable compound is 1 ° C. or higher. How to make a golf ball. The production of the golf ball according to claim 1, wherein the crosslinkable compound having two or more polymerizable unsaturated bonds in the molecule (c) is a crosslinkable compound having two or more (meth) acryloyl groups in the molecule. Method. The crosslinkable compound having two or more polymerizable unsaturated bonds in the molecule (c) is trimethylolpropane tri (meth) acrylate, ethylene glycol di (meth) acrylate, and 1,6-hexanediol di (meth). ) The method for producing a golf ball according to claim 1 or 2, which is at least one selected from the group consisting of acrylate. The content of the crosslinkable compound having two or more polymerizable unsaturated bonds in the molecule (c) in the rubber composition for a core is 2 parts by mass with respect to 100 parts by mass of the base rubber (a). The method for manufacturing a rubber ball according to any one of claims 1 to 3, which is ~ 39 parts by mass. The invention according to claim 1 to 4, wherein the temperature difference (Td-T2) between the molding temperature (T2) in the second step and the 1-minute half-life temperature (Td) of the crosslinking initiator (d) is 40 ° C. or less. How to make a golf ball. Claims 1 to 5 in which the content of the (d) crosslinking initiator in the rubber composition for a core is 0.1 part by mass to 5 parts by mass with respect to 100 parts by mass of the (a) base material rubber. The method for manufacturing a golf ball according to any one of the above. The method for producing a golf ball according to claim 1 to 6, wherein in the first step, (e) a metal compound is further kneaded. The method for producing a golf ball according to any one of claims 1 to 7, wherein in the first step, the kneading temperature at the time of preparing the rubber composition is 95 ° C. or higher and 125 ° C. or lower. The method for producing a golf ball according to any one of claims 1 to 8, wherein the homopolymerization temperature (Tc) of the (c) crosslinkable compound by heat is 120 ° C to 300 ° C.

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